The present invention relates in general to apparatus for replacing buried pipe. It relates in particular to an apparatus which may be drawn through an existing buried pipe to fracture and expand the pipe while simultaneously drawing a replacement pipe into the space previously occupied by the existing pipe.
Distribution systems for utilities, such as water and gas, include a network of pipelines which may be buried under paved highways, streets, or sidewalks. It is often necessary to replace one or more pipes in a distribution network, either to replace a damaged section of pipe, or to replace an existing pipe with a larger pipe having greater throughput capacity.
It is preferable to replace pipes which are buried under paved highways, streets, or sidewalks, with minimum disturbance of the surface under which they are buried. Existing pipe networks are often constructed from pipes made of a fracturable material such as a ceramic or cast iron.
For a network such as a gas distribution network modern plastic pipes may now be used. Plastic pipes are flexible and resist breakage due to earth movement which may be created by a subsidence or an earthquake.
Methods have been developed whereby an existing pipe of a fracturable material may be replaced by moving an apparatus through the pipe to fracture it into fragments, and to force the fragments outward to create a space for a replacement pipe which may have a larger diameter than the existing pipe. A length of pipe to be replaced may be accessed by a hole excavated at each end of the length of pipe. A fracturing apparatus may be introduced, via one of the holes, into an open end of the existing pipe, and moved along the path of the existing pipe while new pipe is fed down the hole down into the space created by the apparatus. The new pipe may be moved through the space by drawing it from the other hole. The pipe may be drawn by applying a pulling force, for example, using a cable attached to a winch. The new pipe may be attached to the pipe fracturing apparatus. When such a method is used, it is not generally necessary to dig a continuous trench to replace a pipe. This may reduce road repair costs and save time spent laying new pipe.
Certain types of pipe fracturing apparatus, and methods for using the same, are disclosed in U.S. Pat. Nos. 4,505,302, 4,720,211, 4,732,222, 4,738,565, 4,886,396, and 5,013,188. The methods disclosed rely primarily on a pushing-force to activate the pipe fracturing apparatus. The pushing-force may be continuous, for example, applied by a hydraulic ram. The pushing-force may also be intermittently or percussively applied, for example, by a pneumatically driven mechanism. A pulling force may be applied to such apparatus only to maintain the direction of advance of the fracturing apparatus through the existing pipe, and to draw the replacement pipe behind the apparatus.
In practice, certain problems may be encountered when operating hydraulic or percussive driven apparatus. Fracturing apparatus which is percussively driven may be directionally unstable. Directionally unstable apparatus may veer from the desired direction of motion down the existing pipeline. This may cause pipe fragments and debris to build up in front of the apparatus to such an extent that it may not be possible to advance it further, or to correct its direction of motion, by applying a pulling force. When this happens, it is usually necessary to dig a hole to locate the fracturing apparatus, and to restart the replacement process from this hole. This may significantly increase the time and cost of pipe replacement.
When drawing a replacement pipe, it is preferable to protect a front portion of the replacement pipe. This may be done by enclosing it with a rigid sleeve included in the fracturing apparatus. In pneumatically driven apparatus, it is difficult to provide a simple means whereby an adequate length of pipe can be quickly and easily drawn into the apparatus to protect it.
Accordingly it is an object of the present invention to provide a pipe replacement apparatus which may be driven by a pulling force only.
It is another object of the present invention to provide a pipe replacement apparatus which is directionally stable.
It is yet another object of the present invention to provide a pipe replacement apparatus which does not cause build up of debris in its direction of travel.
It is a further object of the present invention to provide a pipe replacement apparatus which protects the replacement pipe and may be quickly and easily attached thereto.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combination particularly pointed out in the claims.